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Every human being, with the exception of the nonweight-bearing infant, is vulnerable to the development of corns and calluses, because the skin is subjected to regular mechanical stress. The prevalence of corns and calluses can be readily appreciated by the number of nonprescription products aimed at reducing or preventing them—a billion-dollar market annually.

The earliest known discussion of these lesions can be found in the writings of Cleopatra, who authored a textbook on cosmetics.1 Corns and calluses have plagued humankind since antiquity, affecting those at all socioeconomic levels.

Corns and calluses result from the prolonged application of excessive mechanical shear or friction forces to the skin. In theory, these forces induce hyperkeratinization, which leads to a thickening of the stratum corneum, although the precise mechanism by which this occurs remains unknown. If the abnormal forces are distributed over a broad area (i.e., more than 1 cm2), a callus develops. In contrast, a corn will form if the same forces are applied to a focused location, with the lamellae of the stratum corneum becoming impacted to form a hard central core known as the radix or nucleus (Fig. 98-1).

Mechanical keratoses are not determined genetically. Heredity does play a role, however, in configuring the individual's skeletal architecture. A family history of bony abnormality or ligamentous laxity predisposes the person to the presence of sites of increased cutaneous friction or shear. The prevalence of these lesions has also proven to be significantly higher in females, certain ethnic groups, and mentally ill patients.2,3

History

Corns and calluses produce painful symptoms often described as burning, especially when the affected area is weight bearing and/or shoes are worn. This discomfort is thought to result from microtearing of the thickened, inflexible skin.